What is the largest number of human beings in space at the same time, and what vessels were they on when it happened?
The record appears to be 13. This has happened at least three times, once in 1995 and twice in 2009.
There are many other interesting records related to human spaceflight. On March 14, 1995, a record number of thirteen people were in space at one time. Seven of them were Americans that were on the STS 67 Endeavour, three cosmonauts were on the Mir space station, and an astronaut from the United States, along with two cosmonauts, were aboard Soyuz TM21.
Soyuz TMA-14: Three people aboard, including space tourist Charles Simonyi and the new Expedition 19 crew for the station which numbers two, a Russian and an American. Launched Thursday and will arrive at the station Saturday morning.
Space Shuttle Discovery: Seven people aboard, returning from the space station after delivering the last pair of U.S. solar wings to the orbiting laboratory, boosting it to full power during their STS-119 mission. The shuttle is due to land Saturday in Florida to end a 13-day spaceflight.
International Space Station: Currently home to three astronauts, one each from the United States, Russia and Japan. Two will return home April 7 with Simonyi to end their Expedition 18 mission.
The population boost came from the influx of seven newcomers aboard the space shuttle Endeavour, which docked Friday at 1:47 p.m. EDT (1747 GMT), and opened its hatch into the station a couple hours later.
"The crew of STS-127 is extremely happy to be here," replied Endeavour's STS-127 commander Mark Polansky. "Thirteen is a pretty big number but it's going to be an outstanding visit for us."
Polansky came with pilot Doug Hurley, and mission specialists Chris Cassidy, Julie Payette, Tom Marshburn, Tim Kopra and Dave Wolf. Waiting onboard the station with Padalka were Roman Romanenko, Michael Barratt, Robert Thirsk, Frank De Winne and Koichi Wakata.
The latest record is 19, from December 11, 2021.
- 10 on the ISS with two overlapping SpaceX crews, in orbit.
- 3 on the Chinese Tiangong Space Station, in orbit.
- 6 on Blue Origin's sub-orbital NS-19 flight that lasted 11 minutes.
On July 11th 2021 16 people were in space1 at the same time.
- Seven people on the International Space Station: Three Americans, two Russians, and one from both France and Japan.
- Three Chinese on the Tiangong Space Station.
- Six people on Virgin Galactic's Unity, including Richard Branson, two pilots, and three Virgin Galactic employees.
Note that SpaceX goes to orbit, whereas Virgin Galactic and Blue Origin currently do not. That's worth keeping in mind when considering these records.
1Unity reached a height of 88km, and any flight above 80km is considered space by NASA and the US military. The FAI, though, defines space as beginning at the Karman line 100km above the surface of the Earth.
Jonathan McDowell from the Center for Astrophysics has a very nice overview here: https://planet4589.org/space/astro/web/pop.html
EDIT (12 December 2021): We actually broke the record yesterday. For a few minutes, there were 19 people above the 100 km line. 13 of them were in orbit, 6 were on a sub-orbital flight (maximum altitude 107 km). These were:
- Raja Chari (SpaceX Crew-3), ISS expedition 66
- Thomas Marshburn (SpaceX Crew-3), ISS expedition 66
- Matthias Maurer (SpaceX Crew-3), ISS expedition 66
- Anton Shkaplerov (Soyuz MS-19), ISS expedition 66
- Pyotr Dubrov (Soyuz MS-19), ISS expedition 66
- Kayla Barron (SpaceX Crew-3), ISS expedition 66
- Mark Vande Hei (Soyuz MS-19), ISS expedition 66
- Shane Kimbrough (SpaceX Crew-2), ISS expedition 65
- Megan McArthur (SpaceX Crew-2), ISS expedition 65
- Akihiko Hoshide (SpaceX Crew-2), ISS expedition 65
- Zhai Zhigang (Shenzhou 13), Tiangong space station
- Wang Yaping (Shenzhou 13), Tiangong space station
- Ye Guangfu (Shenzhou 13), Tiangong space station
- Laura Shepard Churchley (NS-19), sub-orbital flight
- Michael Strahan (NS-19), sub-orbital flight
- Dylan Taylor (NS-19), sub-orbital flight
- Evan Dick (NS-19), sub-orbital flight
- Lane Bess (NS-19), sub-orbital flight
- Cameron Bess (son of the former) (NS-19), sub-orbital flight
We almost broke the record this week.
Today (10/11 November 2021), there are 14 people in orbit: 3 Americans, 2 Russians, 1 Frenchman and 1 Japanese on board ISS; 3 Chinese on board the Chinese space station; and the 4 astronauts (3 Americans and 1 German) on Crew-3.
That number would have been 18 if SpaceX had not postponed the launch of Crew-3. As things went, Crew-2 returned with 4 astronauts before Crew-3 could get on the way. The original plan was to have the two missions overlap by several days.
As a side note: The website www.howmanypeopleareinspacerightnow.com used to be a useful tool to answer such questions. Unfortunately, it has been stuck since November, and I'm not sure it will continue to be maintained.